1. Field of the Invention
This invention relates generally to the welding of lead, and more particularly to a process for producing satisfactory lead welds by the use of an arc welding technique.
2. Description of the Prior Art
The joining of two lead members by a butt joint has traditionally been performed by applying heat at the location of the desired joint by using a oxygen-hydrogen torch. At the same time the heat is applied, additional metal from a hand held lead or solder bar is supplied at the joint. Because lead and lead alloys have a low melting temperature (327.4 degrees C. for lead), unskilled use of the torch may cause the lead to completely melt and run off leaving a hole instead of forming the desired joint. As a consequence, one or both of the members to be joined is damaged beyond repair and must be replaced.
It has been possible to join two lead members using the torch where heat can be applied by the torch to both members simultaneously. Thus a butt joint with both members in the same plane can be formed, or a joint with the two members at an angle with their edges adjacent to each other is commonly made. It is also possible, using a torch, to join the edge of one lead member to the surface of another lead member, making a T-shaped joint.
When an attempt is made to join two overlying lead members, however, and heat is applied to the upper member--the upper member will melt and run off before the bottom member becomes hot enough to fuse the two members together. Consequently it has not been possible to form seam joints between two lead members by using the oxygen-hydrogen torch. Also, it has not been possible to make satisfactory lap joints without the use of a filler bar.
A common product formed from lead is flashing which is used on roofs at locations where a pipe or the like passes through the roof. The purpose is to prevent rain water from running down the outside of the pipe and leaking into the building. Lead flashing is particularly useful because it is extremely pliable and can therefore be easily bent to fit over the top of the pipe and to conform to the roof line.
Lead flashing for a pipe is formed from a flat sheet with a circular hole punched from it which is joined to a cylinder. The joint between the flat sheet and the cylinder has been conventionally formed by placing the flat sheet (with the cylinder standing on it centered over the hole) on a horizontally oriented, rotating table. The operator uses the torch to melt a bar of lead or solder so that it forms a bead of supplementary metal completely around the cylinder at its juncture with the flat sheet. The operator controls the rate of rotation of the table by letting it rub against his hand and also holds the torch and the bar of lead or solder in the proper position. If the speed of rotation is too slow or the torch is held too close, a hole will result--ruining the product. If the operator permits the table to rotate too fast or keeps the torch too far from the juncture, fusion between the supplementary metal and the lead sheet and cylinder being joined will not occur.
Some fabrication errors can be corrected after they are discovered, but spoilage and excessive time of fabrication have made production of lead flashing for pipes costly, particularly with unskilled workers. An unskilled worker typically may produce 60 usable flashing products in one eight hour day using this existing technique. Approximately three months of experience are needed before an acceptable level of 500 products per day is achieved.
The low production rate and high spoilage make production by the conventional method expensive because of labor costs. The cost of the additional lead or solder used to make the bead is an added detrimental factor. There are other methods which are currently used, such as using a ring of solder which is positioned at the joint and then melted, and forming the bead on the bottom of the flat sheet, but these have the same objectionable features.
These problems associated with manufacturing lead articles make desirable a more reliable method of joining lead members.
It is therefore an object of this invention to provide a method of welding lead members which is less dependent upon skill than the use of a torch.
It is also an object of this inention to provide a lead welding process which is defined so that reproducible results are possible.
It is a further object of this invention to teach the forming of lap and seam joints by welding between lead members.